Metal flow control

ABSTRACT

A method and a system are for the control of a gas-containing hidden flow of molten metal in a space defined by a tubular device. From measurements in at least one predetermined layer of the metal flow in the space, an indication is obtained of the appearance of the flow which is compared with stored values. The result of the comparison is used for controlling at least one flow-affecting parameter in such a manner that a desired type of flow is provided at least in the layer.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/SE01/02351 which has an Internationalfiling date of Oct. 26, 2001, which designated the United States ofAmerica, and which claims priority on Swedish Patent Application No.0004072-5 filed Nov. 3, 2000, the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to a method and a system for thecontrol of a flow of metal. More preferably, it relates to the controlof a flow of molten metal in a space defined by a tubular device, suchas a pipe and/or, in particular, a pouring nozzle or a submerged entrynozzle.

BACKGROUND OF THE INVENTION

In the metallurgical industry there are different processes in whichliquid metal is to be processed in one way or another. One example isthe casting of metal, such as steel. In part of such a casting process,the liquid metal is supplied from a ladle via a pouring nozzle to atundish. The metal flows from the tundish via a pouring nozzle to acasting mould or chill mould, in which the metal is cooled andtransformed into solid form.

The supply and the flow of the metal through the pouring nozzle is veryimportant in order to produce a configuration of flow in the chill mouldthat gives optimal conditions as regards the solidification of the metaland as regards the use of additives, such as casting powder orlubricant.

Moreover, it is important to prevent solid material, such as aluminiumoxides, from accumulating on the inside of the pouring nozzle and in itsoutlet openings. Such solid material can, on the one hand, causeclogging of the pouring nozzle and the openings and, on the other,affect the flow and thus the casting process and the quality of the endproduct.

By way of today's technique, it is a problem to ensure that a metal flowwhich is located in the pouring nozzle is favorable for the castingprocess, since the metal is hidden or not visible as it flows throughthe pouring nozzle. Attempts are made to estimate what the flow lookslike inside the pouring nozzle by, for instance, water modelling ormathematical modelling. However, these methods mostly take stationaryconditions into account. In reality, marked variations can arise in theflow due to, for example, interference from a flow-controlling unit,such as a stopper or sliding gate, asymmetry in the flow, a varyinglevel in the tundish and clogging of the nozzle.

Usually some form of gas, such as argon, is injected into the pouringnozzle in order to prevent clogging. However, this results in asecondary effect, implying that the flow then can change.

SUMMARY OF THE INVENTION

An object of an embodiment of the present invention is to provide amethod and a system for the control of the metal flow through a definedspace, which will obviate the problems mentioned above.

The above-mentioned object may be achieved according to an embodiment ofthe invention, by a method and a system.

According to one aspect of the invention, a method is thus provided forcontrolling a gas-containing flow of molten metal in a space defined bya tubular device, which may therefore be hidden or not visible, forexample, preferably inside a pouring nozzle or a submerged entry nozzle.The method comprises the steps of

measuring, for at least one predetermined layer of the metal flow in thespace, at least one quantity which is representative of at least oneflow factor in said layer,

obtaining values from the measured quantity, that give an indication ofthe appearance of the flow in said layer by comparing with stored,preferably empirically determined values, and

controlling based on the result of the comparison at least oneflow-affecting parameter, such as gas supply and/or metal supply, sothat a desired type of flow is produced at least in said layer.

According to another aspect of the invention, a system is provided forcontrolling a gas-containing hidden or not visible flow of molten metalin a space defined by a tubular device, preferably inside a pouringnozzle. The system comprises a detection device which is intended to bearranged at the tubular device in order to measure, at least for apredetermined layer in the space, at least one quantity which isrepresentative of at least one flow factor in said layer. An evaluationdevice is connected to the detection device for receiving values whichhave been obtained from the measured quantity and which give anindication of the appearance of the flow in said layer, the evaluationdevice comparing these received values with stored, preferablyempirically determined, values. A control device is connected to theevaluation device and is adapted to control from the result of thecomparison at least one flow-affecting parameter, such as gas supply ormetal supply, so that said desired type of flow is provided in at leastsaid layer.

In this patent application, the flow factor shows itself in componentsactive in the defined space, such as metal contents, gas contents, etc,which each separately or jointly form one or more flow states in thespace.

At least one embodiment of the invention is thus based on theunderstanding that knowledge of the material contents, i.e. thedistribution of materials in the form of metal and gas, in selectedparts of the space, can give information about the actual type of flowtherein. By measuring a quantity which is representative of a flowfactor, such as the metal contents, an indication is obtained of thedistribution of metal and gas in the space. The indication of thedistribution of metal and gas, i.e. the appearance of the flow, isadvantageously obtained by calculation or determination of an indicationvalue which is based on the performed measurements and which is comparedwith stored, calculated or empirically determined values.

In this patent application, type of flow refers to a predetermined,identified appearance, i.e. a predetermined distribution of gas andmetal, in at least some part of a flow. By determining the gas contentsor the gas composition in a predetermined portion of the defined space,it is possible to determine what type of flow is involved in thisportion. Subsequently, the supply of liquid metal and/or, for example,gas to the defined space can be controlled in order to modify theconfiguration of flow in this portion. Consequently, this results in agreat difference compared with prior-art technique, in which it isnecessary to perform rough estimations and in which certain changedconditions can change the configuration of flow considerably withoutbeing discovered directly.

Thus, one advantage of at least one embodiment of the present inventionis that it can continuously take changes into account and controlflow-affecting parameters accordingly. For example, a beginning cloggingcan be discovered at an early stage and be quickly counteracted beforethe interference has become too large.

According to a further aspect of the invention, a flow-controllingsystem as stated above is used for detecting if inclusions/slag whichare/is entrained by the metal accumulate/s on or clog/s a pouringnozzle, and for taking measures that counteract such accumulation ofdeposit/clogging.

Another advantage of at least one embodiment of the present invention isthat a direct procedure is used by measuring on the actual flow unlikeprior-art technique where an indirect procedure in the form of modellingis used.

Essentially three types of flow and combinations thereof as regardsliquid metal in a pouring nozzle have been identified, in the cases whenliquid metal flows through the nozzle and non-metallic material, such asgas, also is present. These three types of flow are: 1) bubbly flow, 2)annular centred flow and 3) annular non-centred flow. In a bubbly flow,supplied gas is diffused or distributed in the metal. An annular centredflow essentially appears in the form of a continuous metal jetsurrounded by gas. The contrary applies to an annular non-centred flowwhere the metal flow essentially follows the walls of the nozzle and agas is located at the centre axis of the nozzle. It may be desirable asregards a predetermined type of flow in a predetermined part of thenozzle. It has among other things turned out to be advantageous to havea bubbly flow in the lower part of the pouring nozzle since this is anessentially constant flow into the chill mould, which favours thecasting process.

An advantageous way of measuring the actual type of flow is to measureon a number of layers or sections in the transverse direction of thedefined space in order to learn what the distribution of material lookslike in these layers. Consequently, it is a question of a type oftomography. By way of the measurement information obtained for therespective layers, it is possible to provide a picture of the flow inselected portions of the defined space and thus determine the actualtype of flow for the respective portions. It should be understood that alayer can be both transverse to the tubular device, i.e. a horizontallayer, and longitudinal, i.e. a vertical layer. A further alternative isdiagonal layers through the tubular device.

At least one embodiment of the invention is extremely useful in castingprocesses, in which liquid metal is supplied from a tundish to a pouringnozzle for teeming into a chill mould. The pouring nozzle in suchprocesses hides the metal flow therein. The absence of insight and thelack of satisfactory possibilities of monitoring are thereforecompensated for by at least one embodiment of the present inventionwhich gives information about the distribution of materials in a layerof the flow in the pouring nozzle.

As already mentioned, a desired type of flow is produced by control ofat least one flow-affecting parameter. In this patent application,flow-affecting parameters relate to such parameters that can affect thetype of flow and therefore should not be limited to flow in the sense ofvolume per unit of time, but should relate to the appearance of the flowas such. For example, gas can be supplied in a predetermined manner sothat the appearance of the flow or the type of flow is changed withoutthe quantity of metal flowing through the space per unit of time beingchanged. In addition to controlling the gas supply, controlling themetal supply is an alternative method of changing or maintaining apredetermined type of flow.

The type of flow can thus be affected by changed supply of metal to thedefined space. Consequently, the direction in which or the angle atwhich the liquid metal is supplied can be changed. Alternatively, alarger or smaller volume of metal per unit of time can be supplied byusing a flow-controlling or flow-affecting unit of a suitable type. Incasting a vertically adjustable stopper is a possible flow-controllingunit. When the stopper is lowered it tightens the inlet of the tubulardevice, i.e. a pouring nozzle, whereby metal is prevented from flowingfrom a container, such as a ladle or a tundish, to the pouring nozzle.However, when the stopper is elevated, the metal is allowed to flow tothe pouring nozzle, the volume being dependent on the vertical positionof the stopper.

Another possible flow-controlling unit is a sliding gate, whichcomprises apertured plates that are arranged on one another, and aredisplaced or rotated relative to one another. Thus, when an aperture inan upper plate at least partly overlaps an aperture in a lower plate, ametal flow is allowed through these to the pouring nozzle (the largerthe overlapping, the larger the metal flow). Those skilled in the artwill realise that also other corresponding flow-controlling units arepossible and that these units can control quantity as well as directionof inflow. The metal flow can also be affected for example by thequantity of liquid metal in the tundish and the speed at which new metalis supplied to the tundish being controlled.

In addition, types of flow can be affected by the supply of gas to thedefined space being changed. The quantity of gas which is supplied isvariable, as well as the pressure at which the supply is provided. Alsoposition and direction are factors which are important, i.e. from wherethe gas is supplied and, for example, at what angle to the main flow orto the walls that limit the defined space. Advantageously, the gas issupplied via a gas pipe which extends through the above-describedstopper which thus also functions as nozzle. The gas can also beinjected from an attaching device which is used for attaching a pouringnozzle to a tundish. Alternatively, the tundish or the pouring nozzle initself can be provided with gas inlets at different angles. Examples ofgases which can be used are inert gases, such as argon, etc.

One characteristic of at least one embodiment of the invention is thatthe measurement and the determination of the actual type of flow occurwithout contact relative to the gas and metal flow. The measurement isperformed from at least one side of the defined space, such as from oneside of a pipe that defines the space. However, there are many possibleconfigurations, some of which will be described below.

In order to measure a quantity which is representative of the metal andgas contents in the space, for example electromagnetic methods ofmeasurement can be used, in which the quantity such as an inducedvoltage is preferably related to the strength of the magnetic field.Another alternative is acoustical measurements, such as the use ofultrasound. Yet another alternative is vibration measurements. Furtheralternatives are different forms of radiation measurements, such asX-ray or gamma measurements. Other alternatives are temperaturemeasurements or pressure measurements. A further alternative is speedmeasurements of the metal and gas flow. Those skilled in the art willrealise that a combination of the methods of measurement indicated abovealso is an alternative.

The detection device which is adapted to give information about thecurrent configuration of flow or the type of flow and which is used inat least one embodiment of the present invention preferably comprisesone or more sensors. The sensors for use in connection with themeasurements can be arranged in such a manner that they surround themetal flow completely or partly. The sensors can be arranged in a planetransversely to the main direction of flow of the liquid metal. Besides,the sensors can be arranged along the main direction of flow of themetal, i.e. in several planes. This is advantageous if it is desirableto detect and control different types of flow in different parts of thedefined space. By measurements being performed continuously, data isobtained for such controlling. For example, when it comes to casting itmay be important to know where the transition zone between centred flowand bubbly flow is located in a pouring nozzle, so that it can beensured that there is enough time for the flow to become a proper bubblyflow before the metal flows out into a chill mould.

A method of measurement which has been found to be especiallyadvantageous comprises the use of a sensor arrangement having coilswhich generate electromagnetic fields and which have been arranged roundthe defined space, in which the metal flows. The arrangement suitablycomprises one or more combinations of transmitting coils and receivingcoils. Advantageously, each coil is arranged next to or enclosing thetubular device. One or more transmitters can operate with one or morereceivers. The coils can each operate with one or more frequencies.Thus, at least one first transmitting coil can generate anelectromagnetic field having a first frequency to which at least a firstreceiving coil is tuned, while at least one second transmitting coilgenerates a field having a second frequency to which at least a secondreceiving coil is tuned. This facilitates the separation of differentlyplaced sets of coils. The coils are preferably arranged in such a mannerthat ambient interference is minimised by some coils being reversecoupled and, thus, the basic signal which may contain interference iseliminated. Consequently, essentially only the signal is measured, whichhas been affected by the physical phenomenon to be measured.

One basic arrangement is to have a transmitting coil and two receivingcoils, the receiving coils being placed in such a manner that one ofthem is not essentially affected by the development in the test object,whereas the other is placed so that it is at least partly affected byevents taking place in the test object. Since the receiving coils arereverse coupled or balanced in a state where no influence from the testobject occurs, a zero signal or a minimum signal is obtained, whichserves as a basis from which measurements of the changes taking place inthe test object are detected with a low degree of noise. In order toavoid the risk of phase transitions between the receiving coils whenchanges take place in the test object, the reverse coupling is suitablymade in such a manner that a small signal on one side of the balancepoint is obtained.

At least one embodiment of the invention is thus suited for use inconnection with metal flow control through pouring nozzles. In a basicconfiguration, a transmitting coil is thus arranged on one side of thepouring nozzle for generating an electromagnetic field. A firstreceiving coil is arranged on the other side of the pouring nozzle sothat this is screened by the contents in the pouring nozzle. The pouringnozzle in itself does not essentially affect the electromagnetic fieldsince the pouring nozzle usually is made of a ceramic material. A secondreceiving coil is arranged in such a manner that it is not at allscreened by the contents of the pouring nozzle. The difference instrength between the electromagnetic fields detected by the tworeceiving coils is calculated in order to determine a value whichindicates the actual type of flow. It has been found that a distinctsignal is already achieved by way of the above-described basicconfiguration, so that a satisfactory indication of the appearance ofthe flow is obtained. However, more coils can be added to thisconfiguration. Consequently, the coils can be arranged in differentpositions round the pouring nozzle and in combinations of one or moretransmitting coils with one or more receiving coils, whereby moreextensive information about the configuration of flow in the pouringnozzle is obtained.

As an alternative to the stationarily arranged coils, one possibility isto use movable coils. For example, a stationary transmitting coil isused which is arranged on one side of the tubular device and a receivingcoil which is screened by the metal flow and is scanned or swept along asection of a circular path. Those skilled in the art will realise thatalso the contrary is possible, i.e. a scanning transmitting coil and astationary receiving coil. Yet another possibility is that both thetransmitting coil and the receiving coil are scanned. The receiving coilcan, as in the above-mentioned technique, be reverse coupled to areceiving coil that is not screened.

In order to calibrate the measuring equipment, zero calibration and fullflow calibration, i.e. with only air and only metal, respectively, inthe defined space, are suitably performed. Moreover, calibration iscarried out with respect to the three typical types of mixed flow. Thiscalibration can be performed in a cold state by using a metal rod whichis inserted into the space and thus represents an annular centred flow.In a corresponding way, a metal pipe can be inserted into the space inorder to obtain representation of an annular non-centred flow. In thecase of a bubbly flow, it is possible to use a metal body havingnon-metallic inclusions which correspond to an expected non-metallicstate, such as a state of gas. This can be provided by way of a metal ora metal alloy, such as Wood's metal, and non-metallic balls casttherein, such as glass spheres.

When measuring on a metal flow in a tubular device, it is thus possibleto obtain an indication of the appearance of the flow, i.e. thediffusion or the composition of gas and metal, by comparing with storedvalues which advantageously are determined empirically as stated above.An alternative is to use values of different types of flow determined bycalculations.

An evaluation device is connected to the detection device. Thisevaluation device is adapted to receive signals from, for example,sensors comprised in the detection device, the actual type of flow beingdetermined based on the received signals. The evaluation devicepreferably comprises suitable conventional electronics, hardware andsoftware.

The evaluation device sends information about the actual type of flow toa connected control device. A user can feed the desired type of flow tothe control device. Thus, a comparison can be made continuously betweenthe actual and the desired type of flow. If the types of flow differ,the control device can control at least one flow-affecting, i.e.flow-type affecting, parameter. The control device can, for example,send signals to valve devices or the like. The control device preferablycomprises suitable conventional electronics, hardware and software.

Since at least one embodiment of the present invention relates to amethod and a system for the control of a gas-containing a metal flow,such as a hidden or not visible flow, for example, this does not preventat least one embodiment of the invention from being used when the gassupply takes place passively. Unlike an active supply of gas when theoperator himself chooses to inject gas into the metal flow, it is commonin, inter alia, pouring nozzle couplings that air or other gases fromthe surroundings passively leaks into the metal flow. If an undesiredflow arises in, for instance, such a leakage, this is controlledaccording to at least one embodiment of the invention by flow-affectingparameters, such as by an active supply of gas and metal so that thedesired type of flow is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows parts of a casting plant, one embodiment ofthe present invention being used.

FIG. 2 shows as FIG. 1 parts of a casting plant, an alternativeembodiment of the present invention being used.

FIGS. 3 a–3 f show different alternative configurations ofelectromagnetic detection.

FIG. 4 shows yet another alternative configuration of electromagneticdetection.

FIG. 5 shows an exemplifying block diagram of the measurement andcontrol of the gas and metal contents in a flow in a pouring nozzle.

FIGS. 6 a–6 c and FIGS. 6 a′–6 c′ illustrate different types of flow fora gas-containing metal flow inside a tubular device.

FIG. 7 shows a diagram of how the influence of the types of flow shownin FIG. 6 on an electromagnetic field varies with the frequency of thegenerated field.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows parts of a casting plant 10, in which thepresent invention is used. A tundish 12 of the casting plant 10 is shownwhich contains liquid metal, such as liquid steel. A vertical pouringnozzle 14 is arranged in the bottom of the tundish 12, through whichpouring nozzle the liquid metal can flow down to a chill mould 16. Thepouring nozzle 14 is lowered into or submerged in the chill mould 16 andthe lower end of the pouring nozzle 14 is located under the surface ofliquid metal. In addition, the lower end of the pouring nozzle 14 isprovided with outlet holes in the form of side openings, whereas its endsurface 18 is closed. The side openings are adapted to produce asymmetric flow in the chill mould as the arrows 20 schematicallyillustrate.

A detection device 22 which is included in the system according to theinvention is arranged round the upper portion of the pouring nozzle 14.The detection device 22 is connected to receiving peripheral equipment24 which can comprise an evaluation device and a control device. Basedon the information received by the detection device 22, the peripheralequipment 24 determines if the actual type of flow is acceptable or if aflow-affecting measure has to be taken. It may, for example, bedesirable to detect any incipient clogging of the pouring nozzle 14, inwhich case the type of flow changes. If such a change occurs, aflow-affecting measure is thus taken by the peripheral equipment 24sending signals to a flow-affecting device which in the Figure isillustrated by a stopper 26 functioning in a known manner.

The stopper 26 can, in a lowered position, be made to seal the inlet 30of the pouring nozzle 14, thereby preventing the metal flow from flowinginto the pouring nozzle 14. The stopper 26 can in various elevatedpositions allow the supply of metal in different quantities. A gasconduit (not shown) having a gas outlet is suitably arranged in thestopper so that gas can be supplied to the metal flow, preferablyindependently of the vertical position of the stopper 26.

FIG. 2 shows parts of a casting plant 40, in which an alternativeembodiment of the present invention is used. The parts included in thiscasting plant 40 have been given the same reference numerals asequivalent parts in FIG. 1. Unlike the detection device 22 in FIG. 1which was arranged only round the upper portion of the pouring nozzle,the detection device according to the embodiment shown in FIG. 2comprises a detection device which are arranged at several locationsalong the pouring nozzle. First detection devices 42 are thus arrangedaround the upper portion of the pouring nozzle 14 and second detectiondevices 44 around the lower portion of the pouring nozzle 14. Forreasons of clarity, only these two sets of detection devices areillustrated. However, those skilled in the art realise that it ispossible to arrange more detection devices along the pouring nozzle.

As the detection device 22 in FIG. 1, the detection devices 42, 44 areconnected to receiving peripheral equipment 24 which communicates with aflow-affecting device 26. Information about the type of flow can thus beobtained at two locations along the pouring nozzle 14 by way of theembodiment shown in FIG. 2. For example, this is advantageous when it isdesirable to ensure that the type of flow changes along the pouringnozzle 14. It may be desirable to have an annular centred flow in theupper portion of the pouring nozzle, the gas which flows along the wallsprotecting the pouring nozzle from, among other things, clogging. On theother hand, in order to obtain an even flow in the chill mould 16, itmay be desirable to have a bubbly flow in the lower portion of thepouring nozzle 14. The shown double set of detection devices can also beused for ensuring that the type of flow is the same along the pouringnozzle 14, if desirable.

FIGS. 3 a–3 f show various alternative configurations as regardselectromagnetic detection which has been found to be advantageous whencontrolling a metal flow in an elongated space, such as a pouringnozzle. FIGS. 3 a–3 f show a transmitting coil as a box filled in withstripes and a receiving coil as a blank box. The dashed lines in thesefigures are only intended for illustrating with which receiving coil orreceiving coils located at a distance the respective transmitting coilscommunicate and, as a matter of fact, do not illustrate the propagationof the actual electromagnetic fields, which would make the figuresindistinct.

A basic arrangement is illustrated in FIG. 3 a, a pouring nozzle 50being schematically shown from above as a circle. On one side of thepouring nozzle 50, a transmitting coil 52 is arranged to generate anelectromagnetic field. Adjacent to the transmitting coil 52, a firstreceiving coil 54 is arranged to sense the electromagnetic field whichthe transmitting coil 52 generates. On the other side of the pouringnozzle 50, a second receiving coil 56 is arranged which also is arrangedto sense said electromagnetic field. However, due to its location, thepouring nozzle 50 with its contents, such as liquid metal, will partlyscreen the transmitting coil 52. The second receiving coil 56 willtherefore detect a weaker field than the first receiving coil 54. Byreverse coupling or subtracting the signals from the receiving coils 54,56, the basic signal which may contain interference is eliminated.Consequently, essentially only the signal affected by the type of flowin the pouring nozzle 50 is measured.

FIG. 3 b shows an alternative configuration, in which the transmittingcoil 52 is arranged to generate an electromagnetic field and fourreceiving coils 54, 56, 58, 60 are arranged to receive the field. Two ofthe receiving coils 54, 58 are arranged adjacent to the transmittingcoil 52 and are not screened by the contents of the pouring nozzle 50.The other two receiving coils 56, 60 are arranged on the other side ofthe pouring nozzle 50, of which one receiving coil 56 is arrangeddiagonally to the transmitting coil 52, whereas the second receivingcoil 60 is arranged displaced to the right in the figure. If it isparticularly interesting to perform measurements on one side of thepouring nozzle 50, this is thus an advantageous arrangement. Thetransmitting coil 52 can generate electromagnetic fields havingdifferent frequencies, for example, by being fed with severalfrequencies or by scanning several frequency bands, the receiving coilsbeing tuned in pairs (such as 54–56 and 58–60, respectively) to therespective frequencies so that the fields detected by the receivingcoils can be easily distinguished.

In FIG. 3 c yet another receiving coil 62 which is arranged adjacent tothe transmitting coil 52 and a screened receiving coil 64 have beenadded. This further screened receiver is displaced to the left in thefigure relative to the other screened receiving coils 56, 60, thearrangement of which corresponds to that in FIG. 3 b. By way of thearrangement in FIG. 3 c, a more complete picture of the flow sectionthrough the pouring nozzle 50 is thus obtained. Alternatively, the threescreened receiving coils 56, 60, 64 can be replaced by one singlereceiving coil that scans or moves in an essentially partly circularpath round the pouring nozzle 50.

In order to obtain an even more complete picture of the flow, furtherreceiving coils can be arranged. For example, FIG. 3 d shows fivereceiving coils 54, 58, 62, 66, 70 which are arranged adjacent to thetransmitting coil 52 and five receiving coils 56, 60, 64, 68, 72 whichare screened by the contents of the pouring nozzle 50.

Instead of using only one transmitting coil, it is possible to useseveral transmitting coils as shown in FIG. 3 e. The figure shows threetransmitting coils 80, 82, 84. Each transmitting coil generates anelectromagnetic field, preferably with a frequency that is differentfrom the frequencies with which the other two transmitting coilsgenerate the fields. Six receiving coils are included in thisarrangement, of which three receiving coils 86, 88, 90 are screened bythe contents of the pouring nozzle 50 and three receiving coils 92, 94,96 are not screened. Each transmitting coil 80, 82, 84 thus has arespective receiving coil 92, 94 and 96, respectively, arranged adjacentto itself and a receiving coil 86, 88 and 90, respectively, on thediametrically opposed side of the pouring nozzle 50, these two receivingcoils being tuned to the frequency band that precisely the specifictransmitting coil uses.

FIG. 3 f shows yet another configuration. In this configuration, atransmitting coil 100, two non-screened receiving coils 102, 104 and ascreened receiving coil 106 are used. The two non-screened receivingcoils 102, 104 are reverse coupled to the screened receiving coil 106.

Although all the arrangements shown in FIGS. 3 a–3 f comprise reversecoupled receiving coils, those skilled in the art will realise that ifan acceptable signal is obtained also without reverse coupling, thenon-screened receiving coils can be left out.

FIG. 4 shows yet another alternative configuration as regardselectromagnetic detection. This figure shows a longitudinalcross-section through a pouring nozzle portion 110. A transmitting coil112 is arranged round the pouring nozzle 110 and, in a correspondingmanner, a receiving coil 114 which is placed below the transmitting coilis arranged round the pouring nozzle 110. An electromagnetic field B,which is generated by the transmitting coil 112, propagates inside thepouring nozzle 110 and is attenuated by the contents before the field isdetected by the receiving coil 114. As in FIGS. 3 a–3 f it is possibleto include a receiving coil which detects the electromagnetic fieldwithout influence from the contents of the pouring nozzle in order toobtain a more distinct output signal. According to the arrangement inFIG. 4, the measurement is thus performed in vertical layers unlike thearrangements shown in FIGS. 3 a–3 f, in which measurement is performedthrough the pouring nozzle in horizontal layers.

FIG. 5 shows an exemplifying block diagram of the measurement and thecontrol of the gas and metal contents in a flow in a pouring nozzle 120.The block diagram thus shows a sensor 122 which preferably is of thetype electromagnetic sensor, acoustic sensor, such as ultrasonic sensor,vibration sensor, radiac dosimeter, such as X-ray or gamma gauge,temperature sensor, pressure sensor or speedometer, or a combinationthereof. The sensor 122 passes on a flow-related measuring signal to anevaluation unit 124 which converts the measuring signal to interpretableactual values. These actual values are fed to a control unit 126 whichcompares the actual values with the desired values which are indicatedby a user or a user unit 128 and which have been derived empirically orby calculations. Subsequently, the control unit 126 controlsflow-affecting parameters based on the result of the comparison in sucha manner that the desired type of flow is provided for the layer wherethe measurement has been performed. The block diagram shows this as ametal-flow-affecting unit 130 and two gas-flow-affecting units 132, 134.The two gas-flow-affecting units can, for instance, comprise a gasoutlet which is adapted to eject gas at the walls of the pouring nozzleand, respectively, a gas outlet which is adapted to eject gas centrallyabove the pouring nozzle.

The signal processing does not in itself constitute part of theinvention, but is of such type that those skilled in the art can takethe appropriate measures. For this reason, the signal processing has notbeen described in detail and has only been illustrated schematically inthe example above.

FIGS. 6 a–6 c and FIGS. 6 a′–6 c′ very schematically illustratedifferent types of flow for a gas-containing flow of metal inside asection of a tubular device 140. FIGS. 6 a–6 c show a longitudinalsection of the tubular device and FIGS. 6 a′–6 c′ show for thecorresponding type of flow a cross-section of the tubular device. Themetal is represented by dark portions and the gas is represented bylight portions.

FIGS. 6 a, 6 a′ illustrate a so-called bubbly flow, i.e. a gas 142 isdiffused in liquid metal 144, essentially in bubbly form. FIGS. 6 b, 6b′ illustrate an annular centred flow, i.e. an essentially continuousmetal jet 144 is annularly surrounded by the gas 142. FIGS. 6 c, 6 c′illustrate an annular non-centred flow, i.e. the metal flow 144essentially follows the walls of the tubular device 140 and surrounds agas jet 142 which flows in the centre of the tubular device 140.

FIG. 7 shows a diagram of how the influence of the types of flow shownin FIG. 6 on an electromagnetic field varies with the frequency of thegenerated field. The diagram shows three graphs, graph A illustrating abubbly flow, graph B illustrating an annular centred flow and graph Cillustrating an annular non-centred flow. The diagram shows how,depending on the frequency, a metal and gas flow in a tubular deviceaffects the electromagnetic field which a receiving device detects andgives information about in the form of an output signal. The outputsignal is shown in the diagram as a signal change in percentage relativeto a basic signal at 100 Hz. In this case, basic signal implies that thetubular device is empty, i.e. without any metal therein.

Apparently, it is easy to distinguish the graph B (annular centred flow)from the two other ones. This depends on the fact that the metal jet insuch a centred flow only gives a small cross-section for the magneticfield to penetrate and therefore this gives only a small signal changecompared with the basic signal. The graphs A and C are similar to oneanother. In both cases, the tubular device contains a large metalcross-section, resulting in a considerable screening of the magneticfield, which leads to great signal changes. Although these two graphsare similar to one another, they exhibit considerable differences. Forexample, they intersect at about 550 Hz, after which graph C goes higherthan graph A. This depends on the bubbles in a bubbly flow (graph A)giving better penetration for the magnetic field at higher frequenciesthan does a homogeneous material free from gas.

Although some preferred embodiments have been described above, theinvention is not limited to them. Consequently, it should be understoodthat a number of modifications and variations can be carried out withoutdeviating from the scope of the present invention defined in theappended claims.

1. A method for controlling a gas-containing flow of molten metal in aspace defined by a tubular device, comprising the steps of: measuring,for at least one predetermined layer of the metal flow in the space, atleast one quantity which is representative of at least one flow factorin said layer of said gas-containing flow of molten metal; obtainingvalues from the measured quantity that give an indication of theappearance of the flow in said layer by comparing with stored values;and controlling, based on the result of the comparison, at least oneflow-affecting parameter so that a type of flow of a desired appearanceis produced at least in said layer.
 2. A method as claimed in claim 1,wherein said desired type of flow includes at least one of thefollowing: a bubbly flow, the gas being diffused in the metal flow, acentred flow of molten metal, the gas essentially surrounding the metalflow, an annular non-centred flow of molten metal, the metal flowessentially surrounding the centred gas.
 3. A method as claimed in claim1, wherein said flow factor comprises the metal contents in said layer.4. A method as claimed in claim 1, wherein said flow factor comprisesthe gas contents in said layer.
 5. A method as claimed in claim 1,wherein the step of measuring said quantity comprises measuring in alayer in the transverse direction of the flow in order to obtain anindication of the distribution of the metal and the gas over said layerof flow.
 6. A method as claimed in claim 5, wherein measurements areperformed in several layers, and based on the measurements performed anindication is obtained of the appearance of the flow in the respectivelayers by comparing with the stored values, at least one flow-affectingparameter being controlled based on the result of the differentcomparisons so that a desired type of flow is provided for each layer,at least one of the same type of flow and a combination of differenttypes of flow being provided in the space.
 7. A method as claimed inclaim 1, wherein said at least one parameter comprises at least one of adirect and indirect supply of gas to the space.
 8. A method as claimedin claim 7, wherein the gas is supplied upstream of the metal flow inthe tubular device.
 9. A method as claimed in claim 7, wherein gas issupplied directly to the defined space and the metal flow flowingtherein.
 10. A method as claimed in claim 7, wherein gas is suppliedindirectly to the defined space and the metal flow flowing therein. 11.A method as claimed in claim 1, wherein the step of measuring saidquantity is performed without contact relative to the gas and metal flowfrom at least one side of the defined space.
 12. A method as claimed inclaim 1, wherein the step of measuring said quantity is performedcontinuously, control of said at least one flow-affecting parameterbeing carried out, if required.
 13. A method as claimed in claim 1,wherein measurements are performed on a metal flow in a pouring nozzle,the measurements of said quantity being performed at least at one endportion of the pouring nozzle.
 14. A method as claimed in claim 1,wherein the step of measuring said quantity is performed by way ofelectromagnetic measurements, said quantity being related to thestrength of an electromagnetic field.
 15. A method as claimed in claim14, wherein the step of measuring said quantity comprises: generating anelectromagnetic field next to the defined space and said layer, anddetecting said electromagnetic field affected by the metal and gascontents in said layer, in a position where the defined space with itscontents at least partly screens the generated field; and wherein thestep of determining the actual type of flow comprises, determining avalue, which indicates a predetermined type of flow, based on thedetected electromagnetic field.
 16. A method as claimed in claim 14,wherein the step of measuring said quantity comprises: generating anelectromagnetic field next to the defined space and said layer,detecting said electromagnetic field affected by the metal and gascontents in said layer, in a position where the defined space with itscontents at least partly screens the generated field, and detecting saidelectromagnetic field essentially without influence from the metal andgas contents in the defined space; and wherein the step of determiningthe actual type of flow comprises, calculating the difference in powerof the two detected fields for determination of a value which indicatesa predetermined type of flow.
 17. A method as claimed in claim 15,wherein said screened position is diametrically opposed to the side fromwhich said field is generated.
 18. A method as claimed in claim 15,wherein said screened position is non-diametrically arranged relative tothe side of the space from which said field is generated.
 19. A methodas claimed in claim 1, wherein said at least one parameter comprisessupply of metal to the defined space.
 20. A method as claimed in claim1, wherein detection is made for detecting accumulation of at least oneof deposit on and clogging of a pouring nozzle with at least one ofinclusions and slag entrained by the metal, and wherein measures aretaken in order to counteract the accumulation of at least one of depositand clogging.
 21. The method of claim 1, wherein the method is forcontrolling a gas-containing a flow of molten metal in a space inside apouring nozzle, wherein the step of obtaining values includes obtainingvalues from the measured quantity that give an indication of theappearance of the flow in said layer by comparing with empiricallydetermined values, and wherein the step of controlling includescontrolling, based on the result of the comparison, at least oneflow-affecting parameter including at least one of gas supply and metalsupply, so that a type of flow of a desired appearance is produced atleast in said layer.
 22. A method as claimed in claim 2, wherein saidflow factor comprises the metal contents in said layer.
 23. A method asclaimed in claim 1, wherein said at least one parameter comprises atleast one of a direct and indirect supply of gas to the space withrespect to at least one of volume, pressure, direction and position. 24.A method as claimed in claim 7, wherein gas is supplied directly to thedefined space and the metal flow flowing therein.
 25. A method asclaimed in claim 7, wherein gas is supplied indirectly to the definedspace and the metal flow flowing therein, before the beginning of thespace.
 26. A method as claimed in claim 1, wherein said at least oneparameter comprises supply of metal to the defined space, with respectto at least one of volume and direction.
 27. A system for controlling agas-containing flow of molten metal in a space defined by a tubulardevice, comprising: a detection device, adapted to be arranged adjacentto the tubular device to measure, for at least one predetermined layerin the space, at least one quantity which is representative of at leastone flow factor in said layer of said gas-containing flow of moltenmetal; an evaluation device, coupled to the detection device, forreceiving values obtained from the measured quantity and which give anindication of the appearance of the flow in said layer by comparing withstored values; and a control device, coupled to the evaluation deviceand adapted to control, from the result of the comparison, at least oneflow-affecting parameter so that a type of flow of a desired appearanceis produced at least in said layer.
 28. A system as claimed in claim 27,wherein said desired type of flow includes at least one of thefollowing: a bubbly flow, the gas being diffused in the metal flow, acentred flow of molten metal, the gas essentially surrounding the metalflow, and an annular non-centred flow of molten metal, the metal flowessentially surrounding the centred gas.
 29. A system as claimed inclaim 27, wherein said flow factor comprises the metal contents in saidlayer.
 30. A system as claimed in claim 27, wherein said flow factorcomprises the gas contents in said layer.
 31. A system as claimed inclaim 27, wherein the detection device comprises a first set of meansfor measuring in a first layer transversely to the flow in order toobtain an indication of the distribution of the metal and the gas oversaid layer of flow.
 32. A system as claimed in claim 31, wherein thedetection device also comprises a second set of means for measuring in asecond layer, the evaluation device being adapted to obtain from theperformed measurements an indication of the appearance of the flow inthe respective layers by comparing with stored values, the controldevice controlling from the result of the different comparisons at leastone flow-affecting parameter in such a manner that a desired type offlow is provided for the respective layers, wherein at least one of thesame type of flow and a combination of different types of flow beingprovided in the space.
 33. A system as claimed in claim 27, whereinmeans for controlling the supply of metal to the space are arrangedupstream of the space and controlled by the control device.
 34. A systemas claimed in claim 27, wherein means for controlling the supply of gasto the space with respect to at least one of volume, pressure, directionand position, are arranged upstream of the space, the means beingcontrolled by the control device.
 35. A system as claimed in claim 34,wherein said means for controlling are arranged in direct connectionwith the space and the metal flow flowing therein.
 36. A system asclaimed in claim 34, wherein said means for controlling are arranged inindirect connection with the space and the metal flow flowing therein.37. A system as claimed in claim 27, wherein the detection devicecomprises at least one electromagnetic transmitter and receiver, saidquantity being related to the strength of an electromagnetic field. 38.A system as claimed in claim 37, wherein the detection device comprises:first means for generating an electromagnetic field next to the definedspace and said layer, and second means, arranged in a position where thedefined space with its contents at least partly screens the generatedfield, for detection of said electromagnetic field affected by the metaland gas contents in said layer; and wherein the evaluation devicecomprises, means for determining, from the detected electromagneticfield, a value which indicates a predetermined type of flow.
 39. Asystem as claimed in claim 37, wherein the detection device comprises:first means, arranged next to the defined space and said layer, forgeneration of an electromagnetic field; second means, arranged in aposition where the defined space with its contents at least partlyscreens the generated field, for the detection of said electromagneticfield affected by the metal and gas contents in said layer; and thirdmeans for detecting said electromagnetic field without any influencefrom the metal and gas contents in the defined space, and wherein theevaluation device comprises, means for calculating the difference instrength of the two detected fields in order to determine a value thatindicates a predetermined type of flow.
 40. A system as claimed in claim38, wherein said second means are arranged diametrically opposed to theside on which said first means are arranged.
 41. A system as claimed inclaim 38, wherein said second means are non-diametrically arrangedrelative to the side of the space on which said first means arearranged.
 42. A system as claimed in claim 37, wherein each of saidelectromagnetic transmitters and receivers is arranged around thetubular device, and wherein said electromagnetic transmitters andreceivers are arranged at different locations along the tubular device.43. The system as claimed in claim 27, wherein the system is used fordetecting accumulation of at least one of deposit on and clogging of apouring nozzle with at least one of inclusions and slag entrained by themetal and for taking measures that counteract the accumulation of atleast one of deposit and clogging.
 44. The system as claimed in claim27, wherein the system is for controlling a gas-containing flow ofmolten metal in a space defined by inside a pouring nozzle; wherein theevaluation device, coupled to the detection device, is for receivingvalues obtained from the measured quantity and which give an indicationof the appearance of the flow in said layer by comparing withempirically determined values; and wherein the control device is adaptedto control, from the result of the comparison, at least oneflow-affecting parameter including at least one of gas supply and metalsupply, so that a type of flow of a desired appearance is produced atleast in said layer.
 45. A system as claimed in claim 27, wherein meansfor controlling the supply of metal to the space with respect to atleast one of volume and direction, are arranged upstream of the spaceand controlled by the control device.